1. Field of the Invention
The present invention relates to adaptors, interfaces, and connectors used to couple an electrical signal to an electrical component receiving the signal.
2. Description of the Related Art
There is a need to provide connection between signal sources and signal sinks, i.e. components receiving the electrical signal from the source. For example, a signal generator may generate a 10 Gb/S RF modulation signal, which is carried via coax cable to a modulator driver of a high speed laser module used for telecom applications. The driver helps to generate a modulated output laser beam which has a modulation obtained from the modulation signal.
At such high frequencies, it is important to provide for impedance matching for optimal electrical return loss, to minimize signal reflections and to optimize system performance. In general, impedance matching means that the impedance of the external device (sink), as well as the transmission line, matches that of the source. Improper impedance matching can lead to excessive distortion and noise problems such as signal reflection. Thus, transmission lines such as coaxial cables are often used for high-frequency RF signals, to provide uniform and matched impedance between the signal source and sink.
However, the connections between the end of the transmission line and the end component receiving the signal often introduce unwanted impedance into the signal path, thus causing signal reflection and adversely affecting system performance. For example, in a high speed laser module telecom application, the coax cable from the output of the signal generator is plugged into the receiving (input) end of an adaptor or connector such as an RF connector, by a standard coax type interface. The output side of the RF connector has an unshielded center pin. When the connector is inserted into the appropriate receptacle of the laser module housing, the center pin (typically about 0.7 mm in length) is wire bonded to the modulator driver (signal sink). The driver uses the RF modulation signal carried by the coax cable to modulate a laser beam.
The coax cable can be designed to have a uniform impedance such as 50.OMEGA., which matches an input impedance of 50.OMEGA. of the modulator driver. However, there will be an air gap between the face of the RF connector, along the exposed, unshielded length of the center pin, to the modulator driver. This mismatching will introduce unwanted signal reflections and other undesirable effects, thus degrading system performance.
Previous attempts to address this problem involve use of discrete adaptors and interfaces from the end user's RF signal to the end component receiving the signal. However, using an increased number of pieces reduces overall performance, and results in higher cost and more complex end product manufacturing. Further, when discrete components are used, there is always an interface issue with associated performance degradation. Discrete components also increase performance variation.